Unlike many other languages, both second/third person singular/plural pronouns are the same in English!

We have both a singular and plural “you” and “they”

If you’re not also going to complain about plural you, ya don’t get to complain about singular they.

Plus, I bet you use the singular they all the time

“Has the mailman come yet?” “No, they haven’t”

You’re not worried about grammar, ya’ll just want to hate on nb people for no reason